The manual says it is needed for the online-help or so. Anyway I need it to do the install.
Checking the server-install I found the OracleText component already installed on my server. After some googling I knew that the OracleText is stored in the schema CTXSYS. Remembering that schema from some other DBs I checked their install-scripts and found a context.sql. This site confirmed me and so I got to SQL+ and run: